Lubricant and method of lubricating metal during forming operations



Patented Aug. 9, 1938 PATENT OFFICE LUBRICANT AND METHOD or LUBRICATINGMETAL DURING FORMING ornrm'rrons Harley A. Montgomery, Highland Park,Mich.

No Drawing. Application May 17, 1934, Serial N0. 726,177

7 Claims.

This-invention relates to a method of drawing or conflgurating metal atsubstantially atmospheric temperature by high pressures and moreparticularly to a method of lubricating the metal in relation to theforming dies during the configurating operations.

It has been conventional in the past to employ lubricating compounds formetal drawing or configurating operations; These compounds have had tobe of anature such that they were easily applied to the metal,lubricated adequately during the configurating operation, and likewisecould be readily removed from the metal after the conclusion of theconfigurating operation. These three properties are of outstandingimportance but other properties are likewise requisite. Altogether thereare ten required charactertistics for lubricants adapted for metalconfigurating and particularly for deep drawing.

1. Film strength-The lubricating film or coating must be strong enoughto withstand the enormous pressure prevailing within the plastic rangeof the worked material under compression, so as to preventmetal-to-metal contact both 5 under static and "flow conditions of theworked metal. Scoring and abrasion of the dies and work-piece must beprevented, as well as pickups of the softer metal on the hardened diesurface. It is generally agreed that where two 30 rubbing surfaces areof the same metal, without an interposing lubricating film, scoringandpickups" are the result of actual fusion of the microscopic surfaces indirect contact, due to the intense localized heat generated fromfriction, even though the duration of the phenomenon is only momentary.Aside from the heat due to rubbing friction of the metallic surfaces,there is also generation of heat due to the plastic deformation of themetal worked, and it is essential that the 40 lubricating film must notbe unduly thinned down and weakened at the higher temperature.

2. oilinesal'he coeflicient of friction between the die surface andwork-piece must be low, so that a minimum amount of energy be expended 5in skin friction, both in the forward or working stroke and in thebackward or pull-back movement of the dies. Lack of oiliness in thelubricant used results in localized drawing, or in uneven elongation andwall thickness. When 50 working on steel sheets of light gage,especially in fianging operations, fracture of the metal and developmentof seams and cracks should be reduced to a minimum when a good lubricantis used.

3. Adhesiveness and spreading.--'I'he lubricant 55 must adhere to thesurface of the metal without being unduly tacky. It must also spreaditself under the pressure of the dies in such a way that it will form aprotecting film ahead of the working portion of the die. It should alsobe sufficiently light in body and possess marked affinity for themetallic surface so that it may be applied manually by means of a brushor mechanically by means of an automate spraying device or throughplastic gelatine-like rolls.

4. Ease of cleaning.-As the finished product 10 from the draw press orstamping machine must generally undergo a further process of plating,tinning, galvanizing, lacquering, or painting, it is essential that alltraces of the lubricant used must be easily removed by means of readilyobtainable 15 and cheap cleanser, such as simple mixture of causticsoda. This requirement is generally met in a drawing compound thatemulsifies in water.

5. Noncorrosiveness.--The lubricant must not contain mineral acids ofany kind that may at- 20 tack the worked metal, should the cleansingprocess be delayed for any reason. Nor should there be any tendency topit the surface of expensive dies and machinery used.

6. Stability and unijormity.--'I'he drawing compound must be stable incomposition, and there must be no separation into its component partsduring storage and handling, nor should it become rancid, decomposed orotherwise spoiled. One shipment must be exactly the same as the previousshipment, unless some modification was made in the formula by mutualagreement to meet a special working condition. This requirement islargely a problem of the lubricant manufacturer.

7. Physiological efiect.-The lubricant must be absolutely neutral in itsphysiological effect on the machine operators, and must not contain anyingredients which may lead to poisoning through skin absorption orinhalation of fumes, nor shall 40 it produce such skin diseases aspimples, eruptions, or boilsi As a further precaution, it might bepermissible to introduce into the lubricant a harmless antiseptic-likecreosol.

8. Orion-No perceptible disagreeable odor should be noticed. Theaddition of a perfuming substance to disguise the real odor of thelubricant should be avoided.

9. Efiect of climatic conditions.-There should be no pronounced changeof the consistency or other properties of the lubricant with the usualvariations of temperature and humidity between summer and winterweather.

10. Economy.--'I'he drawing compound must be low in cost. a

In the past it has been conventional to use water soluble oils oremulsions of water soluble oils as drawing lubricants. For many metaldrawing operations these water soluble drawing oils are entirelysuitable and adequate. In many cases pigments or finely divided solidmaterial have been added to these drawing oils to give the lubricatingfilm greater strength. These solid pigments, however, irender removal ofthe lubricant from the work difllcult after the drawing operation. Inrecent years, however, it has become desirable particularly in relationto the fabrication of automobiles to press or draw very large parts bymeans of extremely heavy pressures. It has also become more and moredesirable to impart to the metal by such operations a greater amount ofrelief or configuration than was previously attempted.

Under the very heavy pressures required for this new type of drawing,the ordinary lubricating film breaks and causes the metal either to bedrawn unevenly or to become scored or marked or broken so that the partcannot be used.

In the past graphite has been used to withstand heavy pressures andwhile graphite is suitable as a lubricant, it is very difiicult toremove from the metal after the forming operation, for the reason thatthe heavy pressure grindsit into the surface of the metal.

It is the'object of this invention to provide a method of lubricatingmetal parts to be configurated under heavy pressures which normally tendto destroy or impair the efiicacy of the lubricating films provided bythe normally employed water soluble lubricants.

The preferred method 'of this invention comprises the application ofsolid, fatty material of relatively high melting point to the work whilethe fatty material is in a molten state, then chilling the material onthe work so that it adheres closely to the surface of the work prior tothe forming operation, configurating the metal with the fatty solidlubricant adhering to it, and removing the fatty solid lubricant bymeans of a hot alkaline solution.

In practicing this method it is requisite that the fatty material chosenbe of such nature that it is solid at the highest room temperaturesencountered during normal operation, that is, temperatures approximatingto F. It is likewise requisite that the fatty material chosen besusceptible to removal from the work by a reasonably economic treatment.For instance, if a high melting point neutral fat be employed ratherthan a high melting point fatty acid, the cost of the drawing lubricantitself is lessened, but the cost of removal is increased, due to thefact that a fatty acid is more readily converted into a water solublealkaline soap than is a neutral fat.

In. view of the present price level, high titre commercial stearic acidis believed to be the best solid fatty material adapted for use in thisprocess. Moreover, stearic acid has'the property of providing a filmwhich when in solidfied form on the metal being configurated, stands upunder the most severe pressures. In order to augment the lubricatingpower of the stearic acid a mineral oil may be mixed with it. Forinstance, the drawing compound employed may comprise substantially 65%commercial stearic acid of a titre above 45, and 35% mineral oil of 100Saybolt at 100 1". viscosity.

In producing the drawing lubricant the stearic acid is melted, the oilmixed therewith, after which compound may be poured in the shippingcontainers and allowed to solidify. Prior to its use, compound is meltedand applied to the metal to be configurated by brush, by dipping, or byspraying. Next, the film is either chilled or permitted to cool so thatit assumes the condition of a solid upon the metal to be conflgurated.Next the metal is subjected to the heavy pressure and is drawn, formedor configurated. Next, the work is immersed in ahot, aqueous, alkalinebath for saponifying the stearic acid, thereby removing it together withthe oil from the work which may then be subjected to finishingtreatments of any nature desired.

The invention in its broadest aspects may be said to reside in forming,drawing, or configurating metal by means of dies and heavy pressure whenthe metal is protected by a lubricating film of solid fatty material.From this point of view the stearic acid or equivalent material may beapplied to the work not only in the manner described, but, for instance,by dissolving the fat in a volatile solvent and permittingsolidification by evaporation or applying the stearic acid or equivalentlubricant to the work in finely divided condition in a vehicle andpermitting the initial pressure of the dies to convert the stearic acidfrom finely divided condition to a solid film. The latter method is thesubject-matter of my copending application, Serial Number 726,178, filedApril 23, 1934.

As previously indicated, several materials other than the commercialstearic acid may be used in place of it with good effect. For instance,parafiin wax, Montan wax, ceresin wax, beeswax, as well as neutral fatof high titre may be used. Generally speaking, the removal of suchmaterials is much more difficult than the removal of stearic acid. Othersolid fatty acids of high titre may be used in place of commercialstearic acid, though the latter is recommended for the reasonsindicated.

It is generally advisable to mix mineral oil with the stearic acid.Straight stearic acid may be used but it is recommended that mineral oilbe added. While the previously specified example comprises 65% stearicacid, 35% mineral oil 100 Saybolt at 100 F. viscosity, the proportionsmay be varied so that the formula contains as small a percent of stearicacid as 50%. The mineral oil may range in viscosity from 80 Saybolt at100 F. to 200 Saybolt at 100 F. Vegetable or animal oils may be used inplace of the mineral oil but for economic reasons mineral oil isrecommended at the present time.

It is requisite, however, that the titre of the stearic acid orsubstitute therefor, the quantity and nature of oil employed and thesolvent power of the oil, be so reconciled and adjusted that theresulting film which hardens on the metal to be configurated is a solid,adhering, durable film.

In practicing the present invention the solid lubricant is melted andapplied to the work by dipping, brushing or spraying. The lubricant isthen permitted to solidify upon the work after which the conflguratingoperations are performed. The work is then subjected to a hot, aqueous,alkaline bath, such as, for instance, 10 pounds NaOH dissolved in 100gallons of water, the temperature preferably being held at about 212 F.By this process the metal is thoroughly protected during theconflgurating operations by a lubricant which is readily removed fromthe work after it has served its purpose.

Having described my invention, I desire to be limited only by theensuing claims:

1. A process of lubricating metal during a 75 forming operation, saidprocess, comprising, coating the surface of the metal with a moltenlubricant comprising stearic acid and mineral oil, solidifying the filmof said lubricant on said suriace, forming the metal and then removingsaid lubricant by treatment with a hot aqueous alkaline solution.

2. A lubricant adapted for metal drawing operations under heavypressure, said lubricant consisting of. substantially stearic acid oisciently high titre to provide a solid at to F. and substantially 35%mineral oil.

3. A process of lubricating metal during the forming operation, saidprocess, comprising, coating the surface oi the metal with a moltenlubricant consisting of mineral oil and an ingredient normally solidselected from the group which comprises stearic acid, paramn wax, Montanwax, ceresin wax, beeswax, and high titre neutral lat, solidifying thefilm of said lubricant on said suri ace, forming the metal, thenremoving said lubricant by treatment with a hot, aqueous, alltalinesolution.

it. in a process oi lubricating metal during the forming operation, thestep which comprises,

coating the surface or 'the metal with a molten 5. In the art of formingmetal at substantially atmospheric temperature under heavy pressure,

the step which comprises, coating the surface of the metal to be formedwithva molten lubricant comprising mineral oil and an ingredientselected from the group which consists of stearic acid, paraflin wax,Montan wax, ceresin wax, beeswax, and high titre neutral fat, thensolidifying the film of said lubricant on said surface.

6. A piece of metal adapted to be formed at substantially atmospherictemperature under heavy pressure, the metal having on its surface asolidified coating of stearic acid and mineral oil.

7. In the art of forming metal at substantially atmospheric temperatureunder heavy pressure. the method which comprises, chilling a moltenlubricant comprised of an oleaginous vehicle of the type of mineral oilin which an ingredient selected from the group consisting of stearicacid, ramn wax, Montan wax, ceresin wax, beeswax. and high titre neutralfat, is dissolved, to provide a solid, continuous film on the metalsurface, then forming the metal in the presence of the solid, thenremoving said him from said metal alter the metal has been formed.

